The disclosure relates to a storage device for storing content data and a data output method for the storage device.
There is known a music data reproducing technology using a configuration in which a storage device retaining music data is connected to a Digital to Analog Converter (DAC) and the DAC is connected to a reproducing device. Music data are digital content data which are signals having a Direct Stream Digital (DSD) format or the like. As an example of such a storage device, there is known a storage device configured to have a port based on a Universal Serial Bus (USB) standard and output music data through a USB-DAC which is a kind of DAC connectable to the USB port (see, for example, fidata for the ultimate in audio quality, from a brand that lives up to the meaning of its name: “reliability” on the Internet URL http://www.iodata.jp/fidata/index.htm).
In the case of outputting music data having the DSD format through the USB port, the previous USB standard has no standard for outputting music data having the DSD format. Therefore, the storage device outputs music data having the DSD format based on a standard called DSD Audio over PCM flames (DoP) via the USB port in compliance with a Pulse Code Modulation (PCM) data format defined in the USB standard.
Recently, the USB-IF (USB Implements Forum) announced a new standard for audio output (see USB_Audio_Specification_USB-IF_ September_2016_FINAL <URL:http://www.usb.org/press/USB-IF_ Press_Releases/USB_Audio_Specification_USB-IF_ September_2016_FINAL.pdf>). According to this standard, when a USB-DAC accesses (negotiates with) the storage device, if the USB-DAC declares that it can convert music data having the DSD format directly into analog data, the storage device can transmit music data having the DSD format to the USB-DAC, without converting the format (hereinafter, this system will also be referred to as the DSD native system). For USB-DACs produced before the announcement of the new standard, the storage device still needs to output music data having DoP format or PCM format through the USB port.
As described above, in the case of outputting music data to a USB-DAC connected to the USB port, the storage device needs to grasp which format of music data the USB-DAC can reproduce, in advance, and output the music data without converting the format or after converting the music data into a format which the USB-DAC can perform digital-to-analog conversion on.
For this reason, whenever connecting a USB-DAC to the USB port of the storage device, a user of the storage device needs to manually set which format of music data the connected USB-DAC can reproduce.
However, this manual setting is cumbersome. In the case of purchasing a new USB-DAC and connecting the USB-DAC to the storage device, the user needs to examine which format of music data the USB-DAC can reproduce, in advance. Therefore, such setting takes a long time.
Also, a technology for configuring a content transmitting device to have information on a format reproducible in a portable player and making the content transmitting device convert contents into the format reproducible in the portable player and transmit the contents to the portable player if the portable player is connected to the content transmitting device was proposed (see Japanese Patent Application Laid-Open No. 2008-47196 for instance). According to this technology, if the content transmitting device transmits a content, the portable player recognizes the format of the content for itself, and reproduces the content.
Meanwhile, in general, USB-DACs as described above do not have the function of recognizing the formats of music data outputted from storage devices, so they covert music data outputted from storage devices into analog data on the assumption that the music data have a predetermined format. Therefore, in the case where such a USB-DAC receives music data having a format different from the predetermined format, conversion into analog data cannot be appropriately performed. Therefore, it is difficult to apply the above-described technology to USB-DACs.